U.S. was told of American's ties to Pakistani militants

Three years before Pakistani terrorists struck Mumbai in November 2008, federal agents in New York City investigated a tip that an American businessman was training in Pakistan with the group that later executed the attack.

The previously undisclosed allegations against David Coleman Headley, who became a key figure in the plot that killed 166 people, came from his wife after a domestic dispute that resulted in his arrest in 2005.

In three interviews with federal agents, Headley's wife said that he was an active militant in the terrorist group Lashkar-i-Taiba, had trained extensively in its Pakistani camps, and had shopped for night-vision goggles and other equipment, according to officials and sources close to the case. The wife, whom ProPublica is not identifying to protect her safety, also told agents that Headley had bragged of working as a paid U.S. informant while he trained with the terrorists in Pakistan, according to a person close to the case.

Federal officials say the FBI "looked into" the tip, but they declined to say what, if any, action was taken. Headley was jailed briefly in New York on charges of domestic assault but was not prosecuted. He wasn't arrested until 11 months after the Mumbai attack, when British intelligence alerted U.S. authorities that he was in contact with al-Qaeda in Europe.

In the four years between the wife's warning and Headley's capture, Lashkar sent him on reconnaissance missions around the world. On five trips to Mumbai, he scouted targets for the attack, using his U.S. passport and cover as a businessman to circulate freely in areas frequented by Westerners. He also met in Pakistan with terrorist handlers.

In March, Headley pleaded guilty to charges of terrorism in the Mumbai attacks and to a failed plot to take and behead hostages at a Danish newspaper. He is cooperating with authorities.

It is not clear from the available information whether a different response to the tip about Headley might have averted the Mumbai attacks. It is known that U.S. anti-terrorism officials warned Indian counterparts several times in 2008 about a possible attack on Mumbai, according to U.S. and Indian officials.

Former DEA informant

The handling of Headley's case calls into question the progress of U.S. law enforcement and intelligence agencies in improving their coordination and the ability to "connect the dots" and deter attacks. It also raises questions about a complicated relationship between U.S. authorities and a confessed terrorist.

Court records and interviews show that Headley served as an informant for the Drug Enforcement Administration, starting in the late 1990s. But a former senior U.S. law enforcement official said Headley's work as an informant ended before the Mumbai attacks in 2008. He could not say whether Headley worked for the drug agency during the years when he was helping to plan the attack.

"Headley was closed as an informant because he wasn't producing anything," the former senior official said. He said he thought Headley's relationship with the DEA ended "years" before Mumbai, but he did not have more precise information.

Federal officials refused to discuss the 2005 tip, other than to confirm that the FBI conducted an inquiry into the allegations made by Headley's wife.

FBI officials said they could not comment on the agency's role in the case because of ongoing prosecutions in Chicago and overseas. A DEA spokesman declined to comment because of a policy against discussing informants. New York police officials confirmed the details of the arrest in the assault case, but they declined to discuss the terrorism inquiry.